1. Field of the Invention
The present invention relates to an organic electroluminescent display device, and more particularly, to an organic electroluminescent display device in which an electromagnetic field preventing and protecting circuit, for protecting internal circuits from abnormal signals having specific characteristics that are generated during manufacturing process or operation, is easily arranged by arranging the electromagnetic field preventing and protecting circuit on a junction region of a flexible printed circuit (FPC) in the organic electroluminescent display device.
2. Description of Related Art
Display devices using light emitting elements including organic electroluminescent (EL) device have actively been developed lately. The organic EL device is suitable for a display device having a thin profile and enhanced viewing angles since backlight required in liquid crystal display devices is not required as the organic EL device is a self-emitting display device.
A type of organic EL device has a structure in which an organic thin film layer is formed between the anode that is a transparent electrode such as ITO and the cathode fabricated using a metal having low work function such as Ca, Li and Al. When a forward voltage is applied to the organic EL device, holes and electrons are respectively injected from the anode and the cathode, the injected holes and electrons are combined to form excitons, and the excitons are emitted and recombined to cause electroluminescence.
An organic electroluminescent display device 100 using the above-referenced organic EL device is illustrated in FIG. 1, which is a plan view for showing a conventional organic electroluminescent display device.
The organic electroluminescent display device 100 includes a substrate 110, a power supply voltage line 120, a pixel region 130, a scan driver 140, a data driver 150, a flexible printed circuit (FPC) 160, a cathode voltage line 170 and an input part 190.
The pixel region 130 is laid up on the substrate 110, and an image is displayed on a front surface of the pixel region 130. The power supply voltage line 120 is used to transmit a power supply voltage to the pixel region 130, and the cathode voltage line 170 is used to supply a cathode voltage to the pixel region 130. The scan driver 140 outputs selection signals to the pixel region 130, and the data driver 150 outputs data signals to the pixel region 130. The FPC 160 is connected to the input part 190 of the respective power supply and cathode voltage lines 120, 170 as well as signal lines to transmit external signals.
As illustrated in FIG. 1, the organic electroluminescent display device 100 is formed by depositing respective wirings and drivers on the substrate 110. The power supply voltage line 120 in the respective wirings is arranged on the outskirts of the pixel region 130 to transmit the power supply voltage to the pixel region 130. In addition, the cathode voltage line 170 is connected to the pixel region 130 at one side of the pixel region 130 so that the cathode voltage is transmitted to the pixel region 130. The scan driver 140 is formed at the other side of the pixel region 130, and the data driver 150 is formed at a position adjacent to the input part 190 of the organic electroluminescent display device 100.
Therefore, when a driving control signal is transmitted to the scan driver 140 and the data driver 150 from the FPC 160, the scan driver 140 and the data driver 150 apply selection signals and data signals, respectively, to the pixel region 130 according to the driving control signal applied. Since unit pixels (not shown) of the pixel region 130 are turned on according to the applied selection signals and data signals, the power supply voltage and the cathode voltage, respectively, of the power supply voltage line 120 and the cathode voltage line 170 are applied to the pixel region 130 so that the respective unit pixels emit light of certain colors.
The organic electroluminescent display device 100 is exposed to electrostatic discharge having high instantaneous voltage by various causes. Since gate insulation film breakage or junction sparking of metal oxide semiconductor (MOS) field effect transistor device inside a semiconductor device is generated under the circumstances, the device is completely broken or finely damaged so that reliability of the device is severely influenced. Therefore, it is important to design to prevent the gate insulation film breakage or junction sparking during the development stage of the organic electroluminescent display device.
In order to solve this problem, an electromagnetic field preventing circuit for preventing damage of internal circuits, created by connecting diodes between signal line and power line of the organic electroluminescent display device and discharging static electricity through the diodes has been suggested as illustrated in FIG. 2.
FIG. 2 is a plan view for showing an arrangement of one such conventional electromagnetic field preventing circuit.
As illustrated in FIG. 2, a plurality of thin film transistors are diode-connected in a conventional electromagnetic field protecting circuit 180. The conventional electromagnetic field protecting circuit 180 is connected between the input lines 191 of the power supply line or the signal line at a region outside the junction (or coupling) region of the FPC 160 and the input part 190 of the organic electroluminescent display device 100.
The electromagnetic field protecting circuit 180 equalizes charge of both sides by discharging charge generated at one side having higher charge to the other side if a charge difference is generated in which one side of the neighboring lines or one side of the same line has higher charge during manufacturing process while the other side has lower charge. Further, the electromagnetic field protecting circuit 180 prevents damage of internal circuits due to instantaneous voltage by discharging a residual voltage obtained by subtracting the total threshold voltage of the respective diode-connected thin film transistors from the generated electrostatic discharge from one side of the line to the other side of the line when electrostatic discharge is generated at one side of line during operation of the organic electroluminescent display device 100.
An arrangement region for the electromagnetic preventing and protecting circuit formed at the input part is limited since region of the input part becomes very crowded as a plurality of signal lines and power supply lines are ordinarily arranged on a limited region of the input part of the organic electroluminescent display device. Further, distances between the wirings are non-uniform due to the mixture of a distance having a wide width between the respective wirings and a distance having a narrow width between the wirings since respective wirings of signal lines and power supply lines of an organic electroluminescent display device are concentrated in a limited region so that the signal lines and power supply lines should be connected to input terminals and pads respectively.
Further, the construction region of the electromagnetic field preventing and protecting circuits is limited since input lines having obtuse angle or acute angle at a certain position are formed in the wirings. Therefore, the electromagnetic field preventing and protecting circuit of a conventional organic electroluminescent display device has problems in that the arrangement region of the electromagnetic field preventing and protecting circuit is very restricted since the electromagnetic field preventing and protecting circuit can be constructed only on a region where respective lines are vertically arranged as illustrated in FIG. 2.